Aluminium is strong, slim and long lasting, but on its own it conducts heat freely. Thermally broken aluminium windows fix that by splitting the frame in two and joining the halves with an insulating strip. Here is how it works, how to read the ratings, and when the cost is worth it in Melbourne.
Key Takeaways
- A polyamide thermal break separates the inside and outside of the frame so heat cannot bridge the metal.
- Uw measures whole-window heat loss and SHGC measures solar gain; choose SHGC by orientation.
- Thermally broken frames with low-E double glazing typically reach Uw 2.0 to 3.0 W/m²K, against 4.0 or more for standard aluminium.
- Victoria’s 7-star NCC requirement makes thermally broken windows the practical choice for new homes and major renovations.
- Expect an indicative premium of 20% to 40% over standard double glazed aluminium, partly offset by lower bills and VEU discounts.
How A Thermal Break Works
Aluminium conducts heat around 1,000 times faster than the polymers used in a thermal break. In a standard frame, winter cold on the outside face travels straight through to the inside, and summer heat does the reverse, so even with double glazing the frame remains a thermal bridge.
A thermally broken frame is extruded as two separate aluminium profiles joined by a strip of glass-fibre reinforced polyamide (PA66, usually 14mm to 34mm wide) rolled in under pressure. It carries structural load but interrupts the heat path completely. Australian manufacturers such as Arch Aluminium Windows and Doors build their thermal ranges on this principle using Alspec framing systems.
The inside face then stays close to room temperature whatever the weather outside, cutting frame heat transfer by roughly 60% to 70%.
Uw And SHGC Explained
Uw is the whole-of-window U-value in W/m²K: heat passing through glass and frame combined per degree of temperature difference. Lower is better. Single glazed standard aluminium sits near 6.0, standard aluminium with double glazing around 4.0 to 4.5, and thermally broken aluminium with low-E double glazing between 2.0 and 3.0.
SHGC, the solar heat gain coefficient, runs from 0 to 1 and measures how much of the sun’s energy comes through. In Melbourne, north-facing glass suits a higher SHGC (0.5 or above) to collect winter warmth, while west-facing glass is better below 0.35 to avoid afternoon overheating.
WERS Ratings Made Simple
The Window Energy Rating Scheme (WERS), run by the Australian Glass and Window Association, rates complete window products from 0 to 10 stars for heating and cooling separately, tied to a specific frame and glass combination. Ask for the certificate for the exact configuration quoted: your assessor needs the certified Uw and SHGC, and VEU only recognises certified products.
Comparing Frame Materials
Indicative Uw figures with double glazing:
- Standard aluminium: Uw 4.0 to 4.5, slimmest frames, lowest cost, frame condensation in winter.
- Thermally broken aluminium: Uw 2.0 to 3.0 with low-E glass, slim frames, large spans, powder coat finish, minimal upkeep.
- uPVC: Uw 1.8 to 2.8, bulkier frames, limited colours and sizes, can distort in strong sun.
- Timber: Uw 2.5 to 3.0, warm look, needs regular painting or oiling, tighter bushfire limits.
Only thermally broken aluminium pairs near-uPVC insulation with slim profiles, large openings and BAL-rated durability. For the range of styles and glazing options, see Arch’s thermally broken thermal windows.
Condensation And Comfort
Condensation forms when warm indoor air touches a surface cooler than its dew point. On a 5°C Melbourne morning, a standard aluminium frame can sit near outside temperature on its inside face, which is why water pools on sills and mould grows on reveals. A thermally broken frame stays warmer, so the dew point is rarely reached and the radiant chill beside the glass disappears.
Meeting 7-Star NCC Rules
The National Construction Code 2022 lifted the minimum rating for new homes from 6 to 7 stars under NatHERS, and Victoria adopted it from May 2024. The extra star is usually won or lost at the windows.
Melbourne assessors often need window Uw values between 2.0 and 3.5 depending on orientation and glass area. Standard aluminium double glazing rarely gets there without shrinking windows, while thermally broken frames let designers keep generous glazing and still pass.
Pairing With Double Glazing
A thermal break does little if the glass is single. Prioritise double glazing first, then a low-E coating, then the thermally broken frame, then argon fill and warm-edge spacers if budget allows. Together they move a window from roughly 6.0 to close to 2.0 W/m²K.
Asymmetric units (6mm outer, 4mm inner) also disrupt more sound frequencies, useful on busy Melbourne roads. Large fixed aluminium windows gain the most from thermal breaking because with no operable sash to leak air, the frame becomes the dominant heat path.
Costs, Rebates And Payback
Across the Australian market, thermally broken aluminium typically costs 20% to 40% more than standard aluminium with the same double glazing: indicatively $900 to $1,500 per square metre supplied and installed, versus $650 to $1,100.
If you are weighing a full replacement, this guide to aluminium window replacement costs shows how frame and glazing choices move the total.
Victorian Energy Upgrades (VEU) offers discounts for replacing single glazed windows with certified energy efficient windows through accredited providers. With heating and cooling savings often quoted at 10% to 25% of energy bills, payback commonly lands within 8 to 15 years, sooner in draughty older homes.
When It’s Worth It
Thermally broken frames make the most sense when building new or renovating under 7-star rules, with large south or west facing glass, where condensation or mould is already a problem, or when you plan to stay long enough to bank the savings.
They are harder to justify on small, well shaded windows in a home you intend to sell soon, or where a thin budget is better spent on ceiling insulation and draught sealing first. In most Melbourne homes with substantial glazing, the comfort gain alone justifies the premium.
FAQ
Do thermally broken windows need double glazing?
Yes, to get any real benefit. The break stops heat crossing the frame, but single glass would still lose most of it. Low-E double glazing is the standard pairing.
Can thermally broken aluminium windows be used in bushfire zones?
Generally yes. Aluminium frames with the right glass and seals can be rated up to BAL-40 under AS 3959, a clear advantage over timber and uPVC on Melbourne’s fringe.
How much do thermally broken windows reduce noise?
The break itself has a small acoustic effect. Most of the reduction comes from the double glazed unit, especially asymmetric or laminated glass, which can cut traffic noise by 30 dB or more.
Will a thermally broken window stop condensation completely?
It removes frame condensation in almost all normal conditions. Glass edges can still fog in humid, poorly ventilated rooms, so bathrooms and kitchens need exhaust fans regardless of window type.
Conclusion
A thermally broken frame closes the gap between aluminium’s strength and the insulation modern Australian homes require. Match it with the right glass, check the WERS certificate, and claim VEU where you qualify. To price a thermal range for your project, request a free quote from Arch Windows.
